Vitamin E
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Vitamin E is a fat-soluble vitamin found naturally in vegetable oils and other fatty foods. The term vitamin E used to be applied generically to 4 tocopherols (α, β, γ, δ) with different antioxidant activities. Today only alpha-tocopherol is considered vitamin E.
Its natural or synthetic form with the highest bioavailability is RRR-α-tocopherol. Commercially available forms normally include both the natural form and the other stereoisomers (8 in total) and are called all-rac-alpha-tocopherol, or their esterified forms such as acetate or succinate. The biological activity, expressed in International Units (IU), of RRR-α-tocopherol compared with all-rac-alpha-tocopherol is 1.49/1 respectively. Efficient absorption of alpha-tocopherol requires the presence of fat. After intestinal absorption, alpha-tocopherol is incorporated into chylomicrons and transported to the liver. There, a specific alpha-Tocopherol Transfer Protein (α-TTP) is responsible for incorporating it into nascent very low-density lipoproteins (VLDL), which are secreted by the liver into the circulation and distributed to the tissues.
Biochemical functions and vitamin E deficiency
Alpha-tocopherol functions mainly as a fat-soluble antioxidant that prevents the propagation of free radical reactions. The vitamin is a scavenger of peroxyl radicals and especially protects the PUFAs of membrane phospholipids and plasma lipoproteins (Wang and Quinn, 1999; Traber and Atkinson, 2007; Niki, 2014). When peroxyl radicals form, they react 1000 times faster with alpha-tocopherol than with PUFAs (Buettner, 1993). By protecting the PUFAs of membrane phospholipids, alpha-tocopherol preserves the integrity and stability of intracellular and cell membranes, plays an important role in the stability of erythrocytes and in central and peripheral nerve transmission, and prevents haemolytic anaemia and neurological symptoms (ataxia, peripheral neuropathy, myopathy, pigmented retinopathy) in individuals lacking alpha-tocopherol (Muller, 1986).
The classification of vitamin E as an essential nutrient is based on animal studies and on primary and secondary alpha-tocopherol deficiency in humans. The need for alpha-tocopherol to prevent foetal resorption in pregnant rats led to the discovery of the vitamin (Evans and Bishop, 1922). The chemical name tocopherol derives from its essential role in reproduction in animals, although this essential role has never been demonstrated in humans (Brigelius-Flohe et al., 2002).
Primary alpha-tocopherol deficiency is an isolated familial condition. Secondary alpha-tocopherol deficiency has been observed in cases of abetalipoproteinaemia, biliary diseases, severe malnutrition, fat malabsorption and cystic fibrosis (Farrell et al., 1977; Jeffrey et al., 1987; Eggermont, 2006; Zamel et al., 2008). Symptomatic alpha-tocopherol deficiency has not been reported in healthy individuals consuming diets low in alpha-tocopherol (IOM, 2000).
The average intake level of alpha-tocopherol with a normal diet for the Italian population (NRV) is 12 mg per day.
(EFSA 2015, mod.)
Volchem produces a concentrated vitamin E supplement in tablets: E-Plus
Its natural or synthetic form with the highest bioavailability is RRR-α-tocopherol. Commercially available forms normally include both the natural form and the other stereoisomers (8 in total) and are called all-rac-alpha-tocopherol, or their esterified forms such as acetate or succinate. The biological activity, expressed in International Units (IU), of RRR-α-tocopherol compared with all-rac-alpha-tocopherol is 1.49/1 respectively. Efficient absorption of alpha-tocopherol requires the presence of fat. After intestinal absorption, alpha-tocopherol is incorporated into chylomicrons and transported to the liver. There, a specific alpha-Tocopherol Transfer Protein (α-TTP) is responsible for incorporating it into nascent very low-density lipoproteins (VLDL), which are secreted by the liver into the circulation and distributed to the tissues.
Biochemical functions and vitamin E deficiency
Alpha-tocopherol functions mainly as a fat-soluble antioxidant that prevents the propagation of free radical reactions. The vitamin is a scavenger of peroxyl radicals and especially protects the PUFAs of membrane phospholipids and plasma lipoproteins (Wang and Quinn, 1999; Traber and Atkinson, 2007; Niki, 2014). When peroxyl radicals form, they react 1000 times faster with alpha-tocopherol than with PUFAs (Buettner, 1993). By protecting the PUFAs of membrane phospholipids, alpha-tocopherol preserves the integrity and stability of intracellular and cell membranes, plays an important role in the stability of erythrocytes and in central and peripheral nerve transmission, and prevents haemolytic anaemia and neurological symptoms (ataxia, peripheral neuropathy, myopathy, pigmented retinopathy) in individuals lacking alpha-tocopherol (Muller, 1986).
The classification of vitamin E as an essential nutrient is based on animal studies and on primary and secondary alpha-tocopherol deficiency in humans. The need for alpha-tocopherol to prevent foetal resorption in pregnant rats led to the discovery of the vitamin (Evans and Bishop, 1922). The chemical name tocopherol derives from its essential role in reproduction in animals, although this essential role has never been demonstrated in humans (Brigelius-Flohe et al., 2002).
Primary alpha-tocopherol deficiency is an isolated familial condition. Secondary alpha-tocopherol deficiency has been observed in cases of abetalipoproteinaemia, biliary diseases, severe malnutrition, fat malabsorption and cystic fibrosis (Farrell et al., 1977; Jeffrey et al., 1987; Eggermont, 2006; Zamel et al., 2008). Symptomatic alpha-tocopherol deficiency has not been reported in healthy individuals consuming diets low in alpha-tocopherol (IOM, 2000).
The average intake level of alpha-tocopherol with a normal diet for the Italian population (NRV) is 12 mg per day.
(EFSA 2015, mod.)
Volchem produces a concentrated vitamin E supplement in tablets: E-Plus
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